The automotive industry is continually researching the combustion process of an internal combustion engine to improve a fuel economy and emissions thereof. To optimize performance of the engine, it is important to be able to control the engine on a cycle-to-cycle basis. For engines operating without a conventional spark ignition, commonly known as the homogenous charge compression ignition (HCCI) mode, the main challenge is to maintain a stable start of combustion (SOC) when the engine is operated at steady state and transient conditions. The instability of the SOC is mainly due to difficulties in the control of in-cylinder air-to-fuel mixture temperature on a cycle-to-cycle basis.
Presently, prior art engines utilize an intake heater to control intake air temperature and/or an amount of residual exhaust gas (REG) to regulate engine in-cylinder air-to-fuel mixture temperature. However, a disadvantage of using the intake heater is its slow response time caused by a large time constant of the heater and a transportation delay from the heater to the cylinder. The slow response time results in inaccurate temperature regulation during the transient operation of the engine. On the other hand, using REG provides expeditious regulation for in-cylinder air-to-fuel mixture temperature control. However, a rate of in-cylinder residual exhaust gas is uncontrollable, leading to SOC and indicated mean effective pressure (IMEP) variation.
Furthermore, advancements have been made in the various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder of the engine. Such advancements include the introduction of multi-injection fuel systems. One multi-injection fuel system is the dual-injection single-fuel system. The dual-injection single-fuel system includes two fuel injectors for each cylinder. One is a direct injector and the other is a port fuel injector. The dual-injection single-fuel system is designed to improve full load performance of the engine at high engine speed operating conditions.
Another multi-injection fuel system is the dual-injection dual-fuel system. The dual-injection dual-fuel system utilizes two different, but comparable fuels. Typically, due to its high octane quality, ethanol has been used in conjunction with gasoline in a dual-injection dual-fuel system. The benefit of the dual-injection dual-fuel system is the capability to increase the combustion efficiency, while suppressing engine knock. The benefit is derived from directly injecting higher octane ethanol fuel into a combustion chamber of the engine. The ethanol has substantial air charge cooling, resulting from its high heat of vaporization. However, the prior art dual-injection dual-fuel system is limited to injecting gasoline into an intake port of the engine.
It is desirable to produce an internal combustion engine including a plurality of fuel injectors adapted to inject a fossil fuel and an alternative fuel, wherein an efficiency thereof is maximized, and emissions and knock thereof are minimized.